The present invention relates to a display panel, particularly to a luminescent display panel containing organic electroluminescence elements.
There have been various kinds of luminescent display panels, the best known of which is a display panel containing organic electroluminescence elements. In detail, such a display panel includes a transparent organic film on which is formed a fluorescent layer. Such a fluorescent layer will emit light if an electric current is flowing therethrough. The organic film and the fluorescent layer together form the organic electroluminescence elements used in the luminescent display panel.
FIG. 2 is a perspective view schematically illustrating a conventional luminescent display panel which includes a glass transparent substrate 6, a plurality of transparent electrodes 2 made of ITO serving as anodes, an organic layer 3 consisting of a positive hole transporting layer and a luminescent layer, a plurality of metal electrodes 1 serving as cathodes arranged in a direction orthogonal to the transparent electrodes 2. In fact, the transparent electrodes 2, the organic layer 3 and the metal electrodes 1 are successively formed on the substrate 6 by way of vapor deposition, thereby forming a multi-laminated structure In this way, with the organic layer 3 interposed between the transparent electrodes 2 and the metal electrodes 1, a plurality of luminescent sections are thus formed, with each intersection of a transparent electrode 2 and a metal electrode 1 constituting one luminescent unit serving as one picture element.
Further, since the transparent electrodes 2 have a high electrical resistance, a plurality of low resistance bus-lines 7 each consisting of a metal film are interposed between the transparent electrodes 2 and the organic layer 3 so as to compensate the transparent electrodes 2 for their electrical conductivities.
What is used to form a metal electrode 1 is an alloy having a small work function, such as Al alloy, In alloy or Ag alloy. On the other hand, what is used to form a transparent electrode 2 is an electrically conductive material having a large work function, such as ITO (having a work function of about 5.0 eV) or a gold (having a work function of about 5.1 eV). However, when a gold is used to form an electrode, the electrode will become semi-transparent. Further, the bus-lines 7 interposed between the transparent electrodes 2 and the organic layer 3 is made of Cr, Cu, Al, Mo, Ta, or their alloy, Alternatively, such a bus-line 7 may be formed of an Al--Cu--Si alloy.
FIG. 3 is a cross sectional view partially illustrating the luminescent display panel of FIG. 2. As shown in FIG. 3, between picture elements (intersections of the transparent electrodes 2 with the metal electrodes 1) are provided insulating films 9 which are then covered by the organic layer 3. In detail, the insulating films 9 are so arranged that two edge portions of each transparent electrode 2 is covered by the films 9 but the central portion thereof is exposed, resulting in a situation that the two edge portions of each insulating film 9 are suddenly climbing over the transparent electrodes 2.
In this way, by providing an insulating film 9 between every two transparent electrodes 2, it is sure to form a desired insulation between the transparent electrodes 2 and the metal electrodes 1, thereby preventing a possible mistaken light emission on areas other than desired picture elements.
Usually, a luminescent display panel shown in FIG. 3 is manufactured by forming a plurality of transparent electrodes 2 on a glass substrate 6, forming a plurality of insulating films 9 on the glass substrate 6 so as to cover the edge portions of each transparent electrode 2, followed by depositting an organic material and then a metal material to successively form the organic layer 3 and the plurality of metal electrodes 1. However, since two edge portions of each insulating film 9 are formed into vertical walls, presenting a structure which is difficult for the organic material and the metal material to deposit thereon, some areas of both the organic layer 3 and the metal electrode layer 1 will have a smaller thickness X (shown in FIG. 3) than other areas. As a result, these areas of the luminescent display panel fail to give a sufficient luminescent brightness.
Moreover, since some areas of the metal electrodes 1 have only a smaller thickness adjacent to the edge portions of the insulating films 9, it is likely that an outside moisture will invade into the organic layer 3, causing a deterioration in a light emitting quality of the display panel, and causing an increase in non-luminescent area.